CN112199845B - Method for determining quantity and color of spot color ink capable of minimizing chromatic aberration - Google Patents
Method for determining quantity and color of spot color ink capable of minimizing chromatic aberration Download PDFInfo
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Abstract
The invention discloses a method for determining the quantity and the color of spot color ink capable of minimizing chromatic aberration. Detecting XYZ values of color samples of two different ink layer thicknesses, and establishing a linear relation function among the X value, the Y value, the Z value and the ink layer thickness of the color samples; build L * Value, a * Value, b * A relationship function between value and ink layer thickness; and (3) establishing a relation function between the color difference between the color sample and the target color and the thickness of the ink layer, and in the range of the thickness of the ink layer allowed by the printing process, calculating a minimum color difference value and a corresponding ink layer thickness, and when the minimum color difference value is smaller than or equal to the allowed value, controlling printing production by using the ink layer thickness and the chromaticity value corresponding to the minimum color difference and the ink quantity standard and the color standard serving as the payable sample, otherwise, correcting the spot color formula. The method solves the problem of low color matching efficiency caused by judging whether the ink color meets the target requirement only according to the proofing color under the condition of the specific ink layer thickness, and can meet the color matching requirement rapidly by combining with adjusting the ink layer thickness outside the adjusting formula, thereby improving the color matching efficiency.
Description
Technical Field
The invention belongs to the field of printing production, and in particular relates to a method for determining the quantity and the color of spot color ink capable of minimizing chromatic aberration
Background
In addition to color printing, lithographic printing is also largely printing with spot color inks, and is more common especially in the field of packaging printing. The customer generally provides a color sample or designates a chromaticity value as a target color requirement and gives an allowable color difference range, a printing enterprise utilizes basic color ink to allocate spot color ink by means of a computer color matching system and manual experience, then a color spreading instrument is used for printing the color sample, and whether the allocated spot color meets the requirement is judged by detecting the color difference between the color sample and the target color requirement. Accurate blending of spot color ink is a difficult task, and even if a computer color matching system is used for assistance, the spot color meeting the requirements can be obtained through repeated adjustment for a plurality of times by means of manual experience.
Because different ink layer thicknesses can generate different color effects within a certain range, the lithographic printing machine can control the ink layer thickness by adjusting the output ink quantity, print out a sample sheet with the gradually changing ink layer thickness, and select the sample sheet closest to the target color as a payment sample. However, when the color sample is printed by using the color development instrument, the thickness of the ink layer of the printed color sample is generally controlled at a certain conventional set value. If the color of the color sample does not meet the target requirement, the color can be adjusted only by repeatedly adjusting the formula, which is one of the reasons for lower color matching efficiency and higher difficulty. In order to obtain color samples meeting target requirements more quickly, for a spot color ink, one can print two or more color samples with different ink layer thicknesses by controlling the extrusion ink amount of an ink injector, and take the color sample closest to the target color. However, for a spot color formula, since the ink color continuously changes with the thickness of the ink layer, after each color sample with one thickness is printed by the color development instrument, operations such as ink homogenizing, cleaning and the like are needed, a plurality of color samples with different thicknesses are printed, the workload of the operation is increased, and the most reasonable ink amount cannot be found. Therefore, in the process of preparing spot colors, for the spot colors of one formula, in the range of the ink layer thickness allowed by the printing process, whether the minimum chromatic aberration between the current ink and the target color under different thickness conditions meets the spot color tolerance requirement is rapidly determined, the ink layer thickness and the chromatic value at the minimum chromatic aberration are given, and the ink layer thickness and the chromatic value are used as the ink quantity standard and the color standard of a printing sample to control the printing production, so that the production efficiency of preparing and printing the spot colors can be effectively improved.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a special color ink quantity and color determining method capable of minimizing chromatic aberration.
In order to solve the technical problems, the method of the invention specifically comprises the following steps:
step 1, printing a color sample according to the thickness of two ink layers by utilizing an ink combination of a paper to be printed, detecting XYZ values of the color sample, and respectively establishing linear relation functions among X values, Y values, Z values and the thickness of the ink layers of the color sample;
further, the printing of the color samples according to the thickness of the two ink layers means printing the color samples at 80% and 120% with respect to the reference ink amount, respectively.
Further, the linear relation function between the X value, the Y value, the Z value and the ink layer thickness is:
X＝k X h+b X
Y＝k Y h+b Y
Z＝k Z h+b Z
wherein:
b X ＝X 1 -K X ·h 1
b Y ＝Y 1 -K Y ·h 1
b z ＝Z 1 -K Z ·h 1
wherein h is 1 、X 1 、Y 1 、Z 1 Respectively refer to the thickness of the ink layer and the XYZ value, h of the printed color sample at 80% of the reference ink amount 2 、X 2 、Y 2 、Z 2 Respectively referring to the ink layer thickness and XYZ values of the printed color sample at 120% of the reference ink amount, h representing the ink layer thickness;
step 2, according to the XYZ color space to L * a * b * Color ofSpace conversion algorithm, establish L of color sample * Value, a * Value, b * A function of the relationship between the value and the ink layer thickness;
further, the L for creating the color sample * Value, a * Value, b * The relationship function between the value and the ink layer thickness h is:
wherein X is 0 、Y 0 、Z 0 XYZ values for the D50 standard illuminant;
step 3, establishing a relation function between the color difference between the color sample and the target color and the thickness of the ink layer according to a color difference calculation formula and a target color requirement value;
further, the relationship function between the color difference delta E between the color sample and the target color and the thickness of the color sample ink layer is:
wherein the method comprises the steps ofL referring to target color * a * b * A value;
step 4, according to the relation function between the chromatic aberration and the ink layer thickness established in the step 3, taking the ink layer thickness as an independent variable and the chromatic aberration as a dependent variable, in the range of the ink layer thickness allowed by the printing process, calculating a minimum value chromatic value corresponding to the minimum chromatic aberration if the minimum chromatic value is smaller than or equal to a spot chromatic aberration allowed value, and controlling printing production by taking the ink layer thickness and the chromatic value corresponding to the minimum chromatic aberration and an ink quantity reference and a color reference which are taken as a payable sample; and if the minimum color difference value is larger than the spot color difference allowable value, correcting the spot color formula.
The invention has the following beneficial effects:
the method can calculate the minimum color difference which can be achieved by the current ink in the range of meeting the ink layer thickness required by the printing process and compared with the target color and the ink layer thickness required by the minimum color difference by using the color spreading instrument to print the color samples with different thicknesses of the two ink layers, can guide workers to adjust the formula, and can quickly meet the color matching requirement and improve the color matching efficiency by combining with adjusting the thickness of the ink layers.
Drawings
FIG. 1 is a flow chart of an implementation of the present invention.
Detailed Description
The invention is further explained below with reference to the drawings;
when special color ink is prepared by offset printing, in order to ensure that the printing ink color can meet the target color requirement after the printing machine is started, a color sample needs to be printed by utilizing a color spreading instrument, and an IGT C1 offset printing suitability instrument produced by Holland IGT company, a domestic color spreading beautiful ink printing suitability instrument and the like are commonly used in the field. Since the area of the ink application area on the color development instrument is fixed, the color development instrument controls the thickness of the ink layer of the color sample by controlling the volume of the ink injection amount. When printing with a color-developer, the ink layer thickness of the print plate can be calculated from the ink-filled volume of the ink-filler divided by the sum of the surface areas of the ink roller of the color-developer and the print plate, or can be obtained from a user manual of the color-developer by inquiry. Taking IGT C1 offset suitability apparatus as an example, if a printing plate having a length of 35 mm is used, the ink layer thickness on the printing plate surface is 2.53 μm as can be seen from the user manual when the ink injection amount is 0.2 ml. The ink transfer rate from the printing plate to the substrate is related to factors such as printing pressure, absorbency of the paper, etc., and if the ink transfer rate is 70%, the substrate will have an ink layer thickness of about 1.77 microns, and many businesses will inject ink on a regular basis of 0.2 milliliter when printing on coated paper using an IGT C1 offset suitability meter.
Injecting ink respectively with 80% and 120% of the conventional reference ink injection amount, homogenizing with a color spreading instrument, printing, calculating or inquiring to obtain the thickness of the ink layer of the printed color sample, and recording as h 1 And h 2 . For example, the conventional reference ink level is 0.2 ml, the ink layer thickness of the printed color sample is 1.77 microns, and then 80% and 120% of the reference ink level, i.e., 0.16 ml and 0.24 ml, respectively, are filled, and the ink layer thickness of the printed color sample is 1.42 microns and 2.12 microns. The thickness of the detected ink layers is h respectively 1 And h 2 XYZ values of the two color samples are respectively denoted as X 1 Y 1 Z 1 And X 2 Y 2 Z 2 . Since the XYZ value of an ink layer is proportional to the spectral reflectance, and there is an approximate linear relationship between the spectral reflectance and the ink layer thickness in the vicinity of the reference ink layer thickness, it can be considered that the thickness of the printed ink layer of an ink has an approximate linear relationship with the X value, Y value, and Z value of the color sample, respectively, in the general printed ink layer thickness range.
By (X) 1 ,h 1 ) And (X) 2 ,h 2 ) For the coordinate points, a linear relation function between the X value of the color sample and the ink layer thickness h is established:
X＝k X h+b X (1)
in the formula (1):
b X ＝X 1 -K X ·h 1 (3)
similarly, with (Y) 1 ,h 1 ) And (Y) 2 ,h 2 ) For the coordinate points, a linear relation function between the Y value of the color sample and the ink layer thickness h is established:
Y＝k Y h+b Y (4)
in the formula (4):
b Y ＝Y 1 -K Y ·h 1 (6)
in (Z) 1 ,h 1 ) And (Z) 2 ,h 2 ) For the coordinate point, a linear relation function between the Z value of the color sample and the ink layer thickness h is established:
Z＝k Z h+b Z (7)
in the formula (7):
b Z ＝Z 1 -K Z ·h 1 (9)
in the field of printing industry, the D50 standard illuminant is internationally used as a reference white field to realize the process from XYZ color space to L * a * b * Conversion of color space. Considering the limitations of the offset ink color, the ratio of the X, Y, Z values of the color sample to the X, Y, Z values of the reference white field, respectively, is generally greater than 0.008856, thus going from XYZ color space to L * a * b * The conversion formulas of the color space are shown in formulas (10) - (12).
Wherein X, Y, Z and X 0 、Y 0 、Z 0 XYZ values, L of the color sample and the D50 standard illuminant, respectively * 、a * 、b * L of finger colour sample * a * b * Values. Substituting the formulas (1), (4) and (7) into the formula (1)0) In- (12), get:
substituting formulas (13) - (15) into the color difference calculation formula (16):
obtaining:
in the formula (17)L referring to target color * a * b * The value Δe refers to the color difference between the color sample and the target color. In theory, the range of the thickness of the ink layer is 0 to infinity, the color of the ink layer continuously changes along with the increase of the thickness of the ink layer, the color difference between the color sample and the target color does not have a maximum value, and the color difference does not have a minimum value. In practical production, the ink layer thickness needs to be controlled within the allowable range of the printing process, the ink layer thickness h is taken as an independent variable, the chromatic aberration delta E is taken as a dependent variable, and the function delta E (h) is calculated on the ink layer thickness [ m, n]Minimum value within the range. The minimum value of the continuous and derivative function of the element on the closed interval can be obtained by adopting a mature method, for example, firstly, the first derivative delta E '(h) of the function delta E (h) is obtained, then the delta E' (h) is enabled to be equal to 0, and the dwell point value h is obtained x Then comparing delta E (m) with delta E (h x ) The value of delta E (n) and the minimum value is the printing processA minimum color difference value within a range of allowable ink layer thicknesses. If the minimum color difference value is smaller than or equal to the color difference value allowed by the customer, the color of the color sample meets the color matching requirement, the color value is calculated according to the ink layer thickness corresponding to the minimum color difference value and substituted into formulas (10) - (12), the printing production is controlled by using the ink layer thickness and the color value corresponding to the minimum color difference value and the ink quantity standard and the color standard which are taken as printing samples, or the color sample is further taken as a color reference in the printing production by utilizing a color spreading instrument according to the ink layer thickness corresponding to the minimum color difference; if the minimum color difference value is larger than the allowable value of the spot color difference, the spot color formula needs to be corrected, and the steps are repeated.
The thickness of the ink layer allowed by the printing process described above needs to be determined by an ink-dispensing worker according to actual production conditions such as the spot color printing area, the ink absorption of the paper, whether the printing apparatus is attached with a drying device, etc., for example, in general, the thickness of the ink layer for spot color printing of a small area is relative to the reference ink amount h 0 The range of the values is as follows:
50％×h 0 ≤h≤150％×h 0 (19)
the special color printing with large area has stricter requirements on the thickness of the ink layer, so that the large-area ground color is not thick enough due to the fact that the ink layer is too thin, but the ink layer is too thick, the ink is not easy to dry, the set-off is caused, the cost of the ink is increased, and the like, and a printer determines the allowed floating range of the thickness of the ink layer according to the actual production condition, such as the requirements:
80％×h 0 ≤h≤120％×h 0 (20)
while the foregoing has been with reference to the preferred embodiments and principles of the present invention, it will be apparent to those skilled in the art from this disclosure that various changes in the specific embodiments can be made, such as determining the optimum print density of four color inks of offset cyan, magenta, yellow, black, etc., such that the color difference between the four color ink print and the standard color requirements is minimized, which should also be considered as the scope of the present invention.
Claims (4)
1. A method for determining the amount and color of spot color ink that minimizes chromatic aberration, comprising the steps of:
step 1, printing a color sample with the thickness of 80% and 120% of the conventional standard ink injection amount by utilizing an ink combination of a paper to be printed, detecting XYZ values of the color sample, and respectively establishing linear relation functions among an X value, a Y value, a Z value and an ink layer thickness of the color sample;
step 2, according to the XYZ color space to L * a * b * Color space conversion algorithm, creating L of color sample * Value, a * Value, b * A function of the relationship between the value and the ink layer thickness;
step 3, establishing a relation function between the color difference between the color sample and the target color and the thickness of the ink layer according to a color difference calculation formula and a target color requirement value;
step 4, according to the relation function between the chromatic aberration and the ink layer thickness established in the step 3, taking the ink layer thickness as an independent variable and the chromatic aberration as a dependent variable, in the range of the ink layer thickness allowed by the printing process, calculating a minimum value chromatic value corresponding to the minimum chromatic aberration if the minimum chromatic value is smaller than or equal to a spot chromatic aberration allowed value, and controlling printing production by taking the ink layer thickness and the chromatic value corresponding to the minimum chromatic aberration and an ink quantity reference and a color reference which are taken as a payable sample; if the minimum color difference value is larger than the spot color difference allowable value, correcting the spot color formula; the minimum value of the continuous and derivative function of the element on the closed interval is determined by adopting a mature method.
2. A method of determining the amount and color of spot color ink that minimizes chromatic aberration as defined in claim 1, wherein: the linear relation function between the X value, the Y value, the Z value and the ink layer thickness of the color sample is established in the step 1:
x＝k x h+b x
Y＝k Y h+b Y
Z＝k Z h+b Z
wherein:
b x ＝X 1 -k x ·h 1
b Y ＝Y 1 -k Y ·h 1
b Z ＝Z 1 -k Z ·h 1
wherein h is 1 、X 1 、Y 1 、Z 1 Respectively refer to the thickness of the ink layer and the XYZ value, h of the printed color sample at 80% of the reference ink amount 2 、X 2 、Y 2 、Z 2 Ink layer thickness and XYZ values of a printed color sample at 120% of a reference ink amount, respectively; where XYZ values refer to coordinate values of CIE 1931XYZ color space, and h represents ink layer thickness.
3. A method of determining the amount and color of spot color ink that minimizes chromatic aberration as defined in claim 2, wherein: l of set-up color samples described in step 2 * Value, a * Value, b * The relationship function between the value and the ink layer thickness h is:
wherein X is 0 、Y 0 、Z 0 Refers to XYZ values of the D50 standard illuminant.
4. A method of determining the amount and color of spot color ink that minimizes chromatic aberration as defined in claim 3, wherein: the relationship function between the color difference delta E between the color sample and the target color and the color sample ink layer thickness is established in the step 3:
wherein the method comprises the steps ofL referring to target color * a * b * Values.
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| CN100999151A (en) * | 2006-01-12 | 2007-07-18 | 海德堡印刷机械股份公司 | Ink control based on model |
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| CN110189649A (en) * | 2019-05-05 | 2019-08-30 | 苏州胜利精密制造科技股份有限公司 | A kind of printing ink color matching method |
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| JP3912246B2 (en) * | 2001-09-28 | 2007-05-09 | セイコーエプソン株式会社 | Ink composition, ink set, and recording method and recorded matter using the same |
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| CN1505564A (en) * | 2001-03-02 | 2004-06-16 | ������������˹��˾Dba Mgi���� | Printing adjustment system and method |
| CN100999151A (en) * | 2006-01-12 | 2007-07-18 | 海德堡印刷机械股份公司 | Ink control based on model |
| JP2017085266A (en) * | 2015-10-26 | 2017-05-18 | 凸版印刷株式会社 | Color prediction system and color prediction method |
| CN110189649A (en) * | 2019-05-05 | 2019-08-30 | 苏州胜利精密制造科技股份有限公司 | A kind of printing ink color matching method |
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